login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A131371 Number of anagrams of n that are semiprimes. 2
0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 2, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 2, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 2, 0, 1, 0, 1, 0, 0, 1, 1, 0, 2, 0, 2, 1, 1, 0, 1, 1, 1, 2, 1, 0, 0, 2, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 1, 0, 2, 1, 1, 0, 0, 0, 1, 0, 2, 2, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,15

COMMENTS

An anagram of a k-digit number is one of the k! permutations of the digits that does not begin with 0. This is to semiprimes A001358 as A046810 is to primes A000040.

LINKS

Table of n, a(n) for n=1..105.

EXAMPLE

a(123) = 3 because 123 = 3 * 41 is semiprime, 213 = 3 * 71 is semiprime, 321 = 3 * 107 is semiprime, while the other anagrams 132, 231 and 312 have respectively 3, 3 and 5 prime factors with multiplicity.

a(129) = 4 because 129 = 3 * 43 is semiprime, 219 = 3 * 73 is semiprime, 291 = 3 * 97 is semiprime, 921 = 3 * 307 is semiprime, while 192 and 912 have 7 and 6 prime factors with multiplicity.

a(134) = 5 because 134 = 2 * 67 and 143 = 11 * 13 and 314 = 2 * 157 and 341 = 11 * 31 and 413 = 7 * 59 are semiprimes, while 431 is prime.

CROSSREFS

Cf. A000040, A001358, A002113, A046810, A097393.

Sequence in context: A277735 A248911 A116681 * A319195 A003475 A248639

Adjacent sequences:  A131368 A131369 A131370 * A131372 A131373 A131374

KEYWORD

base,easy,nonn

AUTHOR

Jonathan Vos Post, Sep 30 2007

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 5 01:27 EDT 2020. Contains 334828 sequences. (Running on oeis4.)